In Tajikistan, I argued with Arianna about Europe versus the US. It's an old chestnut. Arianna thinks the US is a hideous capitalist maw where the poor sell their kids to Walmart as frozen turkeys. I know the truth -- the US is a glorious country of Freedom, unlike Europe which is inevitably doomed to Euro-Islamo-welfaro-infertili-sclerosis. So, in the spirit of Rousseau's remark in the Social Contract --
"What is the end of political association? The preservation and prosperity of its members. And what is the surest mark of their preservation and prosperity? Their numbers and population."*
-- I bet her that there were more immigrants from the EU to the US than vice versa. "No way", she said. "Five times more", I said, as a proportion of the source area's population. And we bet a dinner on it.
The best estimates of migrant stocks I know come from the Global Migrant Origin Database, which comes out of Sussex IIRC. Actually, for our purposes, OECD stats would be fine. We did the calculations today while waiting for our follow-up vaccinations. (PS: Arianna, Malta is so in the EU; others, therefore these calculations are slightly inaccurate.)
TOTAL IMMIGRANTS FROM EU-27 TO US: 4 730 294.
Divided by EU population, which can't possibly be more than 500 million, so let's say it is that: 0.9%. (Actually, according to Eurostat, it is almost exactly 500 million.)
TOTAL IMMIGRANTS FROM US TO EU-27 ... 571 706. Accidentally including Croatia.
Divided by US population of about 300 million: a paltry 0.19%.
OK, not five times, but four times. I owe you dinner, but the moral victory is mine!
(NB also: not much is changed by excluding Eastern Europe.)
* though Rousseau excluded "naturalisation or colonies" as external aids.